The growth in use of small electrically-powered devices has increased the demand for very small electrochemical cells. Metal-air cells have gained significant popularity because only the anode reaction material need be packaged in the cell, while the cathode reaction material is oxygen, which is drawn from the surrounding environment.
Such small electrochemical cells are usually disc-like or pellet-like in appearance, and are about the size of garment buttons. These cells generally have diameters ranging from less than 6.4 millimeters to about 25 millimeters, and height ranging from less than 3.8 millimeters up to about 15 millimeters.
The small size and the limited amount of electrochemically reactive material which can be contained in such small metal-air cells result in considerable attention being directed to improving the efficiency and completeness of the electrochemical reactions which are used in such cells for generating electrical energy.
In addition, such small cells have limited rate capacity for generating electrochemical output, especially over sustained periods of use. However, technical advances in the appliances which use such electrochemical cells are placing increasing demands on the cells. These increasing demands include demands for increased rate of output of electrochemical power.
Especially with respect to cells used in newer hearing aids, a voltage of about 1.1 volts is required for dependable operation of the hearing aid. As the voltage drops below 1.1 volts, the hearing aid may operate improperly, thereby frustrating the user, or may not operate at all.
The limit on the rate at which an electrochemical cell can produce electrochemical power, under heavy demand situations, is determined in part by (i) the rate at which electrical energy generated in the cell can be transmitted to and through respective electrical conductors and thus to the using appliance, and in part by (ii) the rate at which the electrical energy can be generated by electrochemical reactions within the cell.
It is an object of this invention to provide novel compositions of matter for use within the anode portion of the electrochemical cell.
It is another object to provide novel anodes, including novel anode material compositions, for use within the anode portions of the electrochemical cell.
It is yet another object to provide novel electrochemical cells wherein air ports in the cathode can provide a balance between (i) the need for cathodic air to support the electrochemical reaction against (ii) the need to control moisture loss through evaporation.
Still another object is to provide novel anode material compositions, and corresponding cathode structures, which enable longer sustained periods of power production at a relatively steady voltage of at least 1.1 volts, under heavy drain.
A further object is to provide novel anode material compositions, and corresponding cathode structures, which enable longer sustained periods of power production at a relatively steady voltage of at least 1.1 volts while protecting the electrochemically reactive anode metal from corrosion in the alkaline environment.
A further object of the invention is to provide a novel metal air cell having less voltage drop during the first minute after placement of the cell for initial use and having a higher recovered closed circuit voltage after the initial voltage drop.